Appearing on the two hour ITV Referendum Debate, Ms Sturgeon suggested the former London Mayor was campaigning for Brexit to fulfil his ambition to become Prime Minister.

But two weeks out from the June 23 referendum, Ms Sturgeon also found herself under attack from Leave campaigners who accused her of failing to respect the result of the Scottish independence vote.

Ms Sturgeon’s opponents also taunted her over her previous criticisms of the Remain campaign.

The six strong panel pitted Tory against Tory, emphasising the deep divisions in David Cameron’s party. On the Remain side the First Minister joined by Labour’s Angela Eagle and the Conservative Amber Rudd.

While Mr Johnson led the charge for Leave along with his fellow Conservative Andrea Leadsom and Labour’s Gisela Stuart.

Ms Sturgeon took on Leave’s claim that quitting the EU would free up £350 million per week for the NHS – a hotly disputed figure, because it fails to take account of money sent to back to the UK from Brussels.

“I am staggered that Boris Johnson is standing here tonight still defending this £350 million a week figure,” Ms Sturgeon said. “It is a scandal that is still emblazoned across the campaign bus, because it is an absolute whopper.

“The contribution to the EU that each of us makes every week is less than a pound. But what do we get for that money? We get freedom of travel. We get a single market of 500 million people. We get the chance to co-operate to keep ourselves safer. These are the gains.”

Ms Rudd added she intended to “repaint that bus with a leprechaun on one end and a big rainbow and pot of gold.”

Mr Johnson hit back saying Ms Sturgeon was “keener to be ruled by Brussels than Westminster politicians.”

While Ms Leadsom attacked Ms Sturgeon for her suggestions that Brexit could lead to a second Scottish independence referendum.

Ms Leadsom said: “Despite the people of Scotland voting 55 to 45 saying they want to remain in the United Kingdom. She is determined to have another go because it was the wrong answer. Isn’t that what the EU tries to do? She’s not a democrat.”

When pressed on her plans for a second referendum, Ms Sturgeon dodged the question saying she was putting Scottish independence “to one side” and was not appearing to speculate about what happens in the event of a Brexit vote.

But her fellow Remain campaigner Ms Rudd warned that leaving the EU would result in there being “an issue with the Union”.

Ms Rudd said there was “a danger to the Union” if Britain left.

Making the case for the EU, Ms Sturgeon said membership protected workers’ rights.

“I don’t fancy...the prospect of future perhaps a Prime Minister Boris Johnson with complete freedom to rip up workers’ rights to bin environmental protections to keep blaming foreigners for all the ills of the world. That’s a pretty horrifying thought.”

She added: “The thing is Boris Johnson is not interested in your job. He is only interested in David Cameron’s job.”

Mr Johnson said: “We do not want to see any attrition of the rights of people at work. That’s not what we are campaigning for. We are campaigning to take back control of our economy and legislative system.”

The former Mayor also reminded Ms Sturgeon of her complaints that the Remain campaign was guilty of negativity and miserable scaremongering.

When Ms Rudd quoted Institute for Fiscal Studies figures suggesting Brexit would cost the UK £40 billion by 2020, Mr Johnson used Ms Sturgeon’s own words to ask her if that was “miserable, fear-based or negative?”

The early exchanges were dominated by immigration with Mr Johnson arguing for an Australian-style points system. Ms Sturgeon said EU migrants made a positive contribution to the economy, but admitted that “immigration is causing pressure in some areas on public services”.

“I see that in parts of my own constituency but you know what the answer to that is - to invest in our public services not to impose needless austerity cuts,” she said.